Typically, pipe used to carry water can be made from hydraulic calcareous cement compositions including portland cement, concrete, or asbestos-cement combinations. These materials conventionally can be used alone or as liners for metal or outer casings made from other materials. Such pipe in the past has been chosen for such applications since it exhibited great durability and was economically attractive for such use, particularly in municipal water systems.
The major drawback found in the use of these materials over extended periods of time has been erosion by water and in particular, the erosion caused by low mineral content water, i.e. aggressive water. Specifically, such water tends over time to solubilize small amounts of calcium from the set material, which, if not prevented, can superficially weaken the structure of the surface of the cement in contact with the water and lower its ability to successfully resist the abrasive action of the water flow.
This phenomenon has in the past been successfully arrested by coating the inside of such pipe with an asphaltic composition which is abrasion resistant and adheres well to the inside walls of the pipe for extremely long periods of time in normal use. Such materials have come to be aesthetically undesirable since they can impart an objectionable odor or taste to the water. To overcome this disadvantage several alternatives have been employed. One of the most successful alternatives has been the use of a coating composition made up of a vinyl toluene and alpha methylstyrene copolymer such as described in the patent to Stephen M. Quint, et al., U.S. Pat. No. 3,676,196 issued July 11, 1972. This patent describes applying a coating of such materials to the inside walls of a pipe by spraying a solution of the materials in a solvent such as perchloroethylene, which is then removed by vaporation to create a durable glass-like protective coating for the inside surfaces of the pipe. Again, while the coating is highly successful functionally in this application, the mechanism of solvent evaporation was not preferred since small amounts of the organic solvent, if not completely removed, could be detected in the water.
It is desirable therefore to provide a coating for cementitious pipe that is contacting water that does not have entrapped organic solvents or impart an odor or taste to the water. Further the coating must inhibit dissolution of the calcium at the surface of the pipe in contact with water and exhibit superior adhesion to the cementitious article by remaining in place and intact by resisting the abrasive action of the water moving through the pipe. Such a coating should then prevent erosion of the surface of the pipe in contact with water, particularly aggressive water, and not present any of the aforementioned drawbacks.
While many other materials have proven suitable for waterproofing masonary and the like they have not suggested a solution for the problem of aggressive water leaching calcium ions from cementitious pipe products but have rather concentrated on the problem of imparting water repellancy by providing superficial coatings which created high water contact angles.
The environment for this invention therefore requires an appreciation of the requirements currently necessary for pipe used in municipal water applications and in particular in applications where aggressive waters are present.
It is therefore an objective of this invention to provide an internal coating for pipe which will be used in applications where the coating must provide protection against attack from aggressive water, is abrasion resistant and which is demonstratably inert and imparts negligible odor, color, taste or amounts of other substances to the water.